This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-067229, filed Mar. 9, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a charged particle beam exposure technique for forming a desired pattern on a sample, particularly to a charged particle beam exposure apparatus and exposure method in which a mark formed on a sample is used to adjust positions.
2. Description of the Related Art
An electron beam exposure apparatus shown in FIG. 1 has heretofore been used as an apparatus for forming an LSI pattern on a semiconductor wafer. In FIG. 1, a reference numeral 1 denotes an electron gun, 2a to 2c denote lenses, 3 denotes a first aperture, 4a, 4b denote deflectors, 5 denotes a second aperture, 6 denotes a wafer, 7 denotes a stage, 8 denotes a chip, 9 denotes a mirror, 10 denotes a laser interferometer, 11 denotes a detector, 12 denotes an alignment mark, 13 denotes a reflected electron, and 14 denotes an electron beam. Additionally, in many cases, the deflector 4a for use in selecting a beam position of the second aperture 5 is disposed above and below the second aperture 5 to deflect a beam from an optical axis, and to return the deflected beam to the optical axis, but it is shown here in a simple manner, i.e. only above the second aperture 5.
In the apparatus, when the pattern is exposed on the wafer 6, a relative position of the pattern on the wafer 6 with an optics needs to be adjusted. A method for this adjustment includes: using the mirror 9 and laser interferometer 10 to constantly monitor the position of the stage 7; scanning the alignment mark 12 formed for each chip 8 on the wafer 6 with the electron beam 14; detecting the reflected electron 13 from the mark 12 by the detector 11; and measuring the position of the mark 12.
However, this type of method has the following problems. That is, since the mark is detected for each mark 8 on the wafer 6, as shown by arrows in FIG. 2A, a frequency of stage movement 20 increases. As a result, an exposure throughput decreases. Moreover, by an electron beam scanning 21, a resist on the mark 12 is excessively exposed to light, an insoluble region 22 is generated, and this causes dust generation.
As described above, in the conventional alignment in the electron beam exposure, since the frequency of the stage movement increases, the throughput decreases. Moreover, another problem is that the resist on the mark is excessively exposed to the electron beam scanned for the alignment, the dust generation is caused, and an alignment precision is deteriorated.
Therefore, it has been necessary to realize a charged particle beam exposure apparatus and exposure method in which a resist can be prevented from being excessively exposed to the beam scanned for the alignment, and a throughput and the alignment precision can be enhanced.
According to a first aspect of the present invention, there is provided a charged particle beam exposure apparatus, comprising:
a beam gun which emits a charged particle beam;
a projection optics which shapes the charged particle beam and projects a desired pattern;
an incident energy control circuit which controls an incident energy of the projection optics;
a sample stage loaded with a sample in which an image projected from the projection optics is to be formed, a plurality of first marks are formed beforehand, and a plurality of second marks are exposed to the charged particle beam with a first incident energy by the projection optics in the vicinity of the plurality of first marks;
a detector to detect an electron signal generated from a region including the plurality of first marks and the plurality of second marks, when the region is scanned with a second incident energy different from the first incident energy;
a calculation circuit which calculates a positional shift amount between the plurality of first marks and the plurality of second marks from the detected electron signal;
a correction circuit which corrects positions of the plurality of first marks on the sample based on the calculated positional shift amount; and
an exposure control circuit which aligns the desired pattern based on the corrected positions of the plurality of first marks.
According to a second aspect of the present invention, there is provided a charged particle beam exposure method comprising:
exposing a second mark on a sample to a charged particle beam with a first incident energy based on a position of a first mark formed on the sample beforehand;
scanning a region including the first mark and the second mark with a second incident energy by the charged particle beam;
detecting an electron signal generated from the sample by the scanning;
calculating a positional shift amount of the first mark and the second mark from the detected electron signal;
correcting the position of the first mark on the sample based on the calculated positional shift amount; and
aligning and exposing a desired pattern based on the corrected position of the first mark.